Author: Lining Chen, Zhitao Dai, Shumei Jia, Yajun Jia, Enzhuo Quan π¨βπ¬
Affiliation: Cancer Hospital Chinese Academy of Medical Sciences, Shenzhen Center, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen HospitalοΌ Chinese Academy of Medical Sciences and Peking Union Medical College π
Purpose: This work reviewed 12 patient clinical LRT treatments in physics view including geometric and dosimetric parameters and discussed the pros and cons related to the latter.
Methods: Geometric parameters are vertex number, diameter, center to center (c to c) distance and ratio in GTV volume. Plannings conducted for three type of prescriptions are optimized by VMAT in Eclipse 13.6. Dose distributions are reviewed as specific dose profiles at 3 views. DVH are exported to analyze dose volume metrics, PVDR (D10 to D90 ratio of GTV) and gEUD (with a value set to -5) for GTV.
Results: 5 in 12 of patients are in lattice only prescription (P1), 3 in 12 are in lattice boosted prescription with 95% GTV coverage (P2), and 4 in 12 are in lattice boosted prescription with 95% PGTV coverage (P3). GTV volume is between 85.42 cc and 1759.28 cc. LTV to GTV volume ratio is between 1.11 and 2.81. Lattice vertex is of 1 cm or 1.5 cm diameter, and 2.5 cm to 3 cm or 3 cm to 5.5 cm c to c distance. PVDR is between 1.61 to 22.15. PVDRs for P1 are in great divergence between 2.09 and 22.15 but are consistent between 1.61 and 2.70 for P2 and P3.
Conclusion: PVDR divergence indicates inappropriate application of GTV dose volume metrics to P1. However, specific dose profiles in every view are limited for comprehensive dosimetric evaluation. As 50% prescription dose descent reached inside half the vertex c to c distance is the key point in treatment planning, it is promising to apply the ratio of 95% volumetric dose for a normal volume defined as GTV minus LTV (with half the c to c distance extension) to 95% volumetric dose for LTV as PVDR, which is consistant for different LRT prescriptions.